Personal and network laser printers have become ubiquitous in both home and office environments. An important driver for these placements is the lower cost of the printers. Replaceable cartridges supply laser-printer toner, as well as other components of the electrophotographic process. More robust cartridge components are desired to meet requirements for print speed and cartridge life. A critical component to the electrophotographic process, and thus of the typical printer cartridge, is the organic photoconductor (OPC).
An electrophotographic photoreceptor of the dual-layer, laminate-type is composed of a conductive substrate, a thin charge generation layer (CGL) coated over the substrate, and a much thicker charge transport layer coated over the CGL. Such photoconductors generally are charged negatively. The following discussion relates to this type of photoconductor. In this arrangement, an electrically conductive substrate possessing an appropriate work function is required to accept electrons from the charge generation layer under the influence of an electric field.
In this discussion, the preferred electrically conductive substrate is anodized aluminum. In a preferred embodiment, the substrate is an anodized aluminum cylindrical tube. The charge generation layer is typically less than 1μ in thickness. The purpose of this layer is to generate charge carriers upon absorption of light. The photoactive species in this layer is typically an organic-based pigment with a broad optical absorption spectrum. It is necessary to match the absorption maximum with the wavelength output of the laser in order to generate the pigment excited state via photon absorption. Generation of this excited state is the first step in the photoconductive process.
In a preferred embodiment, the pigment/laser combination is a pigment with an absorption max in the near infrared, and a laser output in this region. In a more preferred embodiment, the combination includes a pigment with absorption max greater than 750 nm, and a semiconductor laser with output wavelength in this region. In a still more preferred embodiment, the pigment is a phthalocyanine with absorption max around 780 nm, and a gallium/aluminum/arsenide (Ga/Al/As) laser tuned to a wavelength output of 780 nm.
The charge transport layer is much thicker than the charge generation layer, typically 15-30μ. The charge transport layer has two functions: (1) to accept the photogenerated charge carriers from the charge generation layer; (2) migrate these carriers through the charge transport layer to discharge the photoconductor surface. The electronically active species in this layer is typically a nitrogen-containing small molecule doped into an inert polymeric matrix. In a preferred embodiment, the charge transport molecule is either a hydrazone or an arylamine, and the polymer is a polycarbonate. In a more preferred embodiment, the charge transport molecule is the triarylamine N,N′-diphenyl-N,N′-di(m-tolyl)-p-benzidene-N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD).
The photoconductor of the type described in the foregoing is an integral part of the electrophotographic process that forms the basis of the laser printer industry. The electrophotographic process comprises the following steps: (1) charging a photoconductive imaging member; (2) latent image formation via selective exposure to monocharomatic light; (3) develop the latent image with toner; (4) transfer the toned image to paper; (5) fuse the toner to paper. Although other steps (e.g. removing untransferred toner from the photoconductor with a cleaner blade) may be included, the five steps described above are central to the technology.
A current, state-of-the-art laser printer cartridge incorporates minor components that allow for printing tens-of-thousands of pages. The present invention addresses an issue arising from the cleaner end-seals. These seals ride on both the top and bottom of the photoconductor surface and are responsible for ensuring that untransferred toner does not escape into the cartridge. The end-seals abrade the photoconductor coating, resulting in a narrow band (1-6 mm) of exposed aluminum about 10 mm from the top and bottom of the photoconductor
This abraded region is outside of the print area. However, when printing in hot or wet environments, the exposed aluminum accepts current from the charge roller. This lowers the charge roll voltage, which produces lower photoconductor charging, resulting in an area of background on the printed page. There remains an unfulfilled need to eliminate end-seal wear on the photoconductor that is (1) easily manufactured, (2) low cost.
The present invention is to the use of a spherical organic particle as an additive to the charge transport layer of an organic photoconductor. Addition of organic particles has been described in the organic photoconductor patent literature. See, for example, U.S. Pat. No. 6,071,660 to Black, et al., and references therein. The use of spherical organic and silicon-based additives has been described in U.S. Pat. No. 4,766,048 to Hisamura.